Few rules dominate the dating world as much as “divide by two and add seven.” But where did that rule even come from, and does it hold up today? Harry looks at the history of the age gaps in relationships and tries to find out whether the math actually works out for couples. We want to know what you think of this show! Go to https://cnn.com/margins to share your feedback. To learn more about how CNN protects listener privacy, visit cnn.com/privacy